An electric wire holding structure includes a plurality of electric wires each including a conductive part provided with a plurality of core wires and an insulating part covering the conductive part. The conductive part includes a rectangular conductive part which is formed at an end of the conductive part to have a rectangular outer shape in a section perpendicular to an extending direction of the electric wires. The rectangular conductive parts of the respective electric wires are bonded together by welding with ultrasonic vibration. The rectangular conductive parts of a plurality of the electric wires are piled in a brick laying manner to be bonded by welding.